Multilayer ceramic capacitors are widely utilized as electronic parts featuring a small size, high capacitance and high reliability, with a number of such capacitors being employed in one electronic equipment. In the recent drive toward small-size, high-performance equipment, there is an increasing requirement to develop multilayer ceramic capacitors to a smaller size, higher capacitance, lower cost, and higher reliability.
The multilayer ceramic capacitors are generally manufactured by alternately stacking layers of an internal electrode-forming paste and a dielectric layer-forming paste by a sheeting or printing method, followed by co-firing.
Dielectric ceramic materials used in prior art multilayer ceramic capacitors or the like have the nature that when fired in a reducing atmosphere, they are reduced into semiconductors. This required to use as the internal electrode material noble metals such as palladium, which do not melt at the temperature at which dielectric ceramic materials are sintered and are not oxidized when fired under an oxygen partial pressure high enough to prevent dielectric ceramic materials from converting into semiconductors. However, the noble metals such as Pd are expensive, imposing a substantial bar against reducing the cost and increasing the capacitance of multilayer ceramic capacitors.
Then, a study is being made on the use of relatively inexpensive base metals such as nickel and nickel alloys as the internal electrode material. In the event where base metals are used as the conductor of internal electrode, the internal electrodes can be oxidized upon firing in air. Therefore, co-firing of dielectric layers and internal electrodes must be effected in a reducing atmosphere. However, firing in a reducing atmosphere causes the dielectric layers to be reduced as mentioned above, resulting in a lower resistivity. Non-reducible dielectric ceramic materials were thus proposed.
Exemplary non-reducible dielectric ceramic materials are (Ca,Sr)(Ti,Zr)O.sub.3 compositions with manganese oxide and silicon oxide added as disclosed in JP-A 63-126117, JP-A 63-289709, JP-A 5-217426, JP-B 5-51127, JP-B 5-51122, and JP-B 5-51124. In these patent publications, manganese oxide is added alone such that Mn substitutes for the (Ca,Sr) site whereas silicon oxide is added either alone or as one component of a compound oxide. Manganese oxide is an additive component for imparting reduction resistance whereas silicon oxide serves as a sintering aid. It is thus concluded that dielectric materials containing manganese oxide and silicon oxide are customarily used for ceramic capacitors having internal electrodes formed of noble metals such as nickel.